Seminar Series Events/Videos

The source of about half of the heaviest elements in the Universe has been a mystery for a long time. Although the general picture of element formation is well understood, many questions about the nuclear physics processes and particularly the astrophysical details remain to be answered. Here I focus on recent advances in our understanding of the origin of the heaviest and rarest elements in the Universe.

There is observational evidence that the X-ray continuum source that creates the broad fluorescent emission lines in some Seyfert Galaxies may be compact and located at a few gravitational radii above the black hole. We consider two scenarios for the X-ray emission. The first possibility is that the X-rays may be produced by particles accelerated in an electrostatic gap at the base of a putative jet.

The detection of gravitational waves from mergers of compact binaries in the first two runs of the Advanced LIGO-Virgo have brought in valuable insights into fundamental physics and astrophysics. The coalescence process sweeping the components through a range of frequencies at highly relativistic velocities, have enabled some of the first tests of general relativity in its highly dynamical and extremely strong field regime. The recent detection of the binary neutron star merger has shed first light on the elusive neutron star equation of state.

Over the last few years gravitational wave (GW) detections have marked
the beginning of a new era of astrophysical observations. When the
emitters include a compact object like a neutron star, the GW signal
is accompanied by emissions in different bands, e.g. X-rays,
gamma-rays, optical and neutrinos. The interpretation of such
multimessenger signals allows us to gain a deeper understanding of the
interiors of compact objects. One main challenge is to link our
knowledge of nuclear interactions to macroscopic properties of dense

The unexpected diversity of planetary systems has posed challenges to our classical understanding of planetary formation. For instance, Jupiter sized planets have been detected with short orbital periods of a few days in misaligned orbits with respect to the spin-axis of their host stars. I will first describe the statistical implication of detecting misaligned hot Jupiters and will suggest how dynamical interactions between an outer perturber and the inner planet, can naturally lead to the formation of such misaligned hot Jupiters.

Conventional equations of state suggest that in complete gravitational collapse a singular state of matter with infinite density could be reached finally to a black hole, the characteristic feature of which is its apparent horizon, where light rays are first trapped. The loss of information to the outside world this implies gives rise to serious difficulties with well-established principles of quantum mechanics and statistical physics.

This talk will explore the applications of the computing power of numerical relativity to gravitational theories beyond general relativity. Specifically, I will consider dynamical Chern-Simons gravity, which has roots in string theory and loop quantum gravity. I will discuss our formalism and efforts to simulate binary black holes in this theory to generate waveforms LIGO and LISA. Additionally, I will discuss the generation of numerical black hole solutions in this theory, and applications to probing black hole shadows with the Event Horizon Telescope.

Black-hole recoils are arguably the strong-gravity phenomena with the most striking astrophysical consequences. In the late inspiral and final coalescence of black-hole binaries, anisotropic emission of gravitational waves causes significant linear momentum loss. The remnant black hole, therefore, recoils in the opposite direction. These final kicks can reach magnitudes up to 5000 km/s (“superkicks”), larger than the escape speed of even the most massive galaxies, thus opening the possibility of black hole ejections.

The recent detections of gravitational waves from compact object binary
lead to detailed investigations of the origin of these objects. In my talk
I will discuss the questions: What is the astrophysical origin of these objects?
What do these detections tell us about the formation of black holes and neutron stars?
What are the main problems that they pose?
What to expect in the coming gravitational observations?

Detections of compact binary coalescences with Advanced LIGO and Advanced Virgo are now starting to become routine. However, thereis still considerably more information that can be gleaned from these observations, particularly as detector sensitivity and waveform modelsboth improve. We start by describing the methods currently used in LIGO/Virgo data analysis to determine the mass and spin of the remnant black hole of the binary black hole coalescences.